The present invention relates generally to the field of perforated articles. More specifically, the present invention relates to a method of fabricating perforated articles in a desired contour or shape.
In many applications, it is desired to form articles of varying shapes with perforations therein, such as acoustic panels for aerospace applications. These panels have been produced from epoxy resin impregnated woven fabrics using a variety of different perforation techniques, such as through drilling. However, drilling is not desirable because such action impairs the load bearing ability of the panels. Accordingly, others have attempted to produce perforations in acoustic panels through molding.
U.S. Pat. No. 4,486,372 teaches one method of making a contoured perforated structure through molding of low flow epoxy resin impregnated woven graphite sheets. In this method, a sheet impregnated with low flow epoxy resin is placed over a mold surface having pins thereon. The sheets are then forced onto the pins and partially cured in the flat configuration of the mold. Thereafter, the partially cured sheets are removed, formed into a desired final configuration and cured again to provide a final cure. Since the method requires forming after partial curing, the partial cure step must not cure the resin so much that the partially cured material cannot be bent into the desired form. On the other hand, the partial cure step must cure the resin sufficiently to prevent the resin from flowing into the perforations upon removal from the mold and to prevent damage or deformation of the sheets upon such removal. However, as far as can be ascertained by the Applicants, if the resin is cured sufficiently to be successfully removed from the studded mold, the material is so rigid that it cannot be successfully formed to produce contoured parts. On the other hand, if the resin is cured sufficiently little so as to be formable into contoured parts, the material cannot be removed without distortion and deformation, resulting in an unacceptable part.
The method of U.S. Pat. No. 4,486,372 attempts to alleviate the foregoing problems by using a low flow resin which is less likely to flow after partial cure. However, the use of low flow resin, which is substantially harder than high flow resin, creates difficulties in forcing the resin impregnated material onto the mold and in smoothing out the material on the mold.